1. Field of the Invention
The present invention relates generally to portable terminal devices and position detection methods used therein, and more particularly to a portable terminal device having a rotatable liquid crystal display part and a position detection method used therein.
2. Description of the Related Art
In recent years, portable terminal devices typified by cellular phones have been more and more diversified and provided with more and more functions with development of data communications. Further, with a dramatic increase in the amount of information processable in portable terminal devices, their display parts (liquid crystal display units) have come to have larger screens. Moreover, there have been provided cellular phones capable of receiving one-segment (one-segment partial reception service) broadcasting, and it is also desired that such cellular phones displaying television pictures have liquid crystal display units with larger screens.
With respect to portable terminal devices typified by conventional cellular phones, it is important to reduce size and weight in terms of portability. Further, in terms of operability, common portable terminal devices have vertically elongated shapes so as to be easy to hold, so that their display parts are commonly disposed in portrait positions in accordance with their shapes. However, in the case of displaying letters or characters on such a display part disposed in a portrait position, the number of letters or characters displayed per line is limited, which makes sentences hard to read. Further, in the case of displaying a television picture on the vertically elongated display part, the screen is reduced in size or a large part of the television picture is not displayed because the television picture is horizontally elongated, thus resulting in inefficiency.
Therefore, there have been provided portable terminal devices in which the display part is rotatable relative to the main body of the device. (for example, see Patent Documents 1 and 2 listed below.) In the case of carrying such portable terminal devices, the display part is in a portrait position so as to maintain portability. On the other hand, at the time of using the display part, for example, displaying a television picture, the display part is rotated to be in a landscape position, thereby improving display characteristics.
In such portable terminal devices where the display part is rotatable relative to the main body of the device, it is necessary to switch the display in accordance with the state (position) of the display part. That is, when the display part is in a portrait position, it is necessary to display a screen with a correct orientation for this position. When the display part is rotated from this position, the screen should also be displayed with a correct orientation for a position to which the display part is rotated.
Therefore, such portable terminal devices where the display part is rotatable relative to the main body of the device have a position detection part configured to detect the position (orientation) of the display unit. The image display part that displays an image on the display part is configured to switch the display so that the image is displayed in accordance with the position of the display part detected by this position detection part.    [Patent Document 1] Japanese Laid-Open Patent Application No. 2003-319043    [Patent Document 2] Japanese Laid-Open Patent Application No. 2005-176372
In many portable terminal devices with a rotating display part as described above, the display part is configured so as to rotate +90° and −90° from a reference position (at which the display part is located when unrotated) serving as a center. Accordingly, the position detection part is required to detect these three states (positions). Methods of this position detection include those using non-contact sensors and those using mechanical switches. Of those, methods using non-contact sensors (for example, magnetic sensors), which are stable over time, are commonly adopted.
Conventionally, in the case of detecting the three states of the display part as described above, sensors should be provided for the corresponding states. Specifically, in the case of using, for example, a magnetic sensor as a sensor, the magnetic sensor and a magnet are provided at each of the position of the unrotated display part, the position to which the display part is rotated +90°, and the position to which the display part is rotated −90°. As a result, the conventional portable terminal device has the problem of an increased number of components and an increased number of interconnects (interconnection lines).